1. Field of the Invention
This invention relates generally to medical lasers, and relates more particularly to a hand-held laser scanner that generates a scanned pattern of constant size regardless of the positioning of the laser scanner with respect to a treatment surface.
2. Description of the Relevant Art
Historically, surgical incisions in tissue have been performed with sharp metal cutting instruments. More recently, lasers have become the tool of choice in many medical procedures to cut and treat tissue. Laser beams can be accurately focused on tissue to cut many desired shapes and depths. The slit incision, a very narrow elongated incision, is especially appropriate for laser surgery. Surgeons can make these narrow incisions by passing a focused laser beam over the target tissue.
One medical procedure where slit incisions are desired is hair transplants. Hair transplants have become a common cosmetic procedure, particularly for the treatment of male pattern baldness. In a hair transplant procedure, a piece of the patient's skin having healthy growing hair is removed from a donor region on the scalp and implanted into a hairless, recipient region. This process involves cutting a hole or slit into the recipient region so that the new plug of hair can be inserted. Slit grafting is modernly used because of its many cosmetic and medical advantages over circular punching.
Historically, slit grafting has been accomplished by cutting a slit into the recipient region with a scalpel. More recently, lasers have been used. A laser is more advantageous because the size and shape of the incision can be more accurately controlled. A laser beam, usually a pulsed infrared beam, is focused onto the scalp. The exposure can be controlled to remove the amount of skin needed for the hair graft dimensions. Another advantage of using lasers to cut or remove skin is the coagulating effects of the laser light that minimizes bleeding and pain. Further, the laser radiation removes the skin in the slit it creates thereby creating room for the new plug of hair to be placed inside. A laser assisted hair transplant method is described in U.S. Pat. No. 5,360,447, which is assigned to Coherent, Inc, the assignee of the present application.
A laser beam can be accurately focused on the scalp by a variety of optical delivery systems. One such system is marketed by Coherent, Inc. in conjunction with its sealed carbon dioxide medical laser system under the name Ultrapulse 5000. To create a slit, the surgeon positions the output of the optical delivery system so that the beam will impinge on the target tissue. The surgeon then presses a footswitch which opens a shutter that allows light to exit the output end of the optical delivery system. The doctor then moves the output end over the target tissue until the desired slit width and depth is created. This procedure is followed for every slit made in the target tissue.
The drawback to this optical delivery system is that it takes time and skill to create a series of slits of the desired dimensions and layout. Since the number of slits required can be as numerous as the number of individual hair follicles being transplanted, the time and skill required to create accurate slits in the recipient area can be great. Furthermore, the placement of each slit is important, because uniform patterns give a more natural appearance of the transplanted hair. Thus, there is a need for an optical delivery system that creates multiple slits in uniform patterns.
Lasers are also used surgically to treat relatively large areas of tissue in techniques such as ablation to remove disfigured skin. The spot diameter of the laser beam is typically larger in size and lower in power density as compared to lasers used to make incisions. Even though the spot diameter of the laser beam is relatively large, the area of treatment is usually larger than the area of the spot, which requires that the beam be scanned or otherwise moved across the area to be treated.
One approach to moving the laser beam across a treatment area is to scan the beam like a raster, back and forth in successive rows until the area is covered. One drawback to that approach is that successive rows can overlap with insufficient recovery time in between scans of successive rows, which can damage the tissue in the areas of overlap. Another drawback is that the pattern area covered by the laser can be dependent on the distance between the treatment area and the scanning device, which is not easily controlled if the laser instrument is handheld by the surgeon.
There is thus a need for an optical delivery system that creates an scanned laser beam in a uniform pattern regardless of the precise position of the treatment surface with respect to the laser instrument.